70 SPIDERS: THEIR STRUCTURE AND HABITS. 



produced, forming the warp ; as these are being drawn out the 

 spinning-tubes of the long upper pair are similarly manipulated to 

 ])repare the woof, which by an alternate lateral movement of the 

 joints is bound down upon^ and across the warp. This process is 

 repeated until the web has acquired the necessary toughness and 

 compactness. 



The best example of British Burrowing Spiders is that very rare 

 species of the Mygaiidcs, and the only one found in Britain, the 

 Atypus Sidzcri, (Plate 7, Fig. 7,) which means by interpretation the 

 mis-shapen one. It loves sandy places, where it excavates for its 

 abode a cylindrical hole half an inch in diameter, in a direction slop- 

 ing downwards. To keep out the sand it lines this hole with a tube 

 of v>'hite silk of compact tissue, protecting the entrance by a flap of 

 the same material, and for this purpose it is furnished with a promi- 

 nent pair of spinnerets like the Agekna labyriiitJiica. This is the only 

 kind of spider that has the fangs of its falces articulated horizontally, 

 so as to give them a vertical movement. They are very formidable 

 weapons, and so gigantic in size that the owner would be unable to 

 see over them but for an adaptation of the cephalothorax to meet 

 the emergency. It carries in its forepart a protuberance or turret, 

 and on the summit of this the eyes are planted in four pairs. 



From a friend I recently received an interesting communication 

 relative to this solitary British species of trap-door spiders. He 

 informs me that a few days before he had dug out the nest of an 

 Atypus^ in the vicinity of London. The tube was 10 inches long, 

 and at the bottom was the female surrounded by her numerous 

 progeny, 157 in number, l^he male was not at home. 



But the cleverest of all the Burrowing Spiders is the Trap-door 

 Spider of Jamaica, who lines her subterranean gallery with a fine 

 silken tube enclosed in one of a coarser texture. The flap at the 

 mouth of this double tube is neatly finished off with a hinge, and 

 is so contrived as to open outwards only, and to close by its own 

 weight when left alone, concealing all traces of the burrow, the outer 

 surface being covered with earth. Specimens of these nests are 

 preserved in the British Museum. 



EXPLANATION OF PLATE YIL 



Fig. 1. — Circulatory sj^stem of Spider. «., The 4-clic'\mbered 

 heart, inclosed iii a pericardium, and sending off 

 arterial branches into tlie cephalothorax ; 6., the 

 gills in which the blood is aerated before it returns 

 to the pericardium through 4 large vessels, as shewn. 



